Covid-19 cases, hospitalizations and deaths are leveling off in hot spots like Seattle and New York. New infections should soon begin to decline, and many parts of the country will be able to start a phased return to “normal.” Yet without a vaccine, normality will look very different than it did before the pandemic.

The medical community and the public are hungry for news about vaccines, but accounts of progress have been exaggerated. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and senior member of the White House coronavirus task force, has put into perspective the overly optimistic predictions of a vaccine available within the target of 12 to 18 months: “A vaccine that you make and start testing in a year is not a vaccine that’s deployable.” There is a world of difference between testing a vaccine candidate and millions of people lining up for a shot.

Clearly, there is a sense of urgency. What, then, is standing in the way of the rapid deployment of a vaccine? For one, unproven technologies—which are being used by virtually all of the Covid-19 vaccine developers—present significant safety concerns. And once researchers have a vaccine candidate, the risk-averse regulators at the Food and Drug Administration get involved. The regulatory process can be sped up, but corners can’t be cut without sacrificing confidence about the safety and efficacy of the product . . .